message: play around with unit testing

I think I am probably going to move unit tests to a separate
directory/file structure. This will allow me to add a bunch of utility
functions that don't get analyzed for the library compilation and also
avoid testing-only imports in the main modules.

build.zig

@@ -33,6 +33,8 @@ pub fn build(b: *std.Build) void {
         .optimize = optimize,
     });
 
+    main_tests.linkLibrary(nats_c);
+
     const run_main_tests = b.addRunArtifact(main_tests);
     const test_step = b.step("test", "Run tests");
     test_step.dependOn(&run_main_tests.step);